Related Rates, water entering trough problem

A trough is 15ft long and 4ft across the top. Its ends are isosceles triangles with height 3 ft. Water runs into the trough at a rate of 2.5 cubic feet per minute. How fast is the water rising when it is 2 feet deep?

A trough is 15ft long and 4ft across the top. Its ends are isosceles triangles with height 3 ft. Water runs into the trough at a rate of 2.5 cubic feet per minute. How fast is the water rising when it is 2 feet deep?

The answer is .0625 but I'm pretty lost on how to get there.

volume of water in the tank ...

using similar triangles ...

solve for , substitute the result for in the volume formula to get as a function of .